The present invention generally relates to apparatus including a cryosurgical probe of the type suitable for destroying diseased or degenerated cells in a living being by freezing such cells, and particularly to a surgical probe for administering a freezing treatment to abnormal cells in areas which may be embedded in or surrounded by healthy body tissue without injury to the healthy body tissue.
Since the introduction of the first cryoprobe by Dr. Cooper in 1964, cryosurgery, or the freezing of tissue for destruction, has steadily grown to become a concrete therapeutic modality in the medical, dental, and veterinary fields. In particular, cryosurgery gained wide acceptance in the gynecological and dermatological specialties. However, the technique has only enjoyed modest success in other areas of medicine, such as urology and neurosurgery. This is undoubtedly related to limitations of the early engineered devices which remain in use today with little modification. Growth of new cryosurgical technology and instrumentation was judged to be at a near standstill following the Eight Annual Meeting of the American College of Cryosurgery in 1988, and it was felt the future growth of cryosurgery depended on the development of high cooling capacity devices with increased precision and the flexibility to be used endoscopically and percutaneously. Current cryosurgical instrumentation employs liquid nitrogen or nitrous oxide as coolant materials, both of which contribute to the existing limitations. Liquid nitrogen is either sprayed onto tissue or circulated to a probe which is applied to tissue. The advantage of liquid nitrogen is its extremely low temperature (-190.degree. C.) which gives it a high cooling capacity. However, liquid nitrogen is evaporated during use, and thus requires continual replacement as well as storage vessels. Other disadvantages of liquid nitrogen systems include: relative complexity of probes which require high vacuum insulation and create problems with miniaturization for endoscopic use, cumbersome to use due to thick insulated hoses which circulate the coolant to the probe and which can become rigid during use, discomfort to the user due to cooling of the probe handle, and cooling of the entire shaft of the probe making the device less ideal for endoscopic procedures due to tissue freezing along the shaft's length.
Nitrous oxide (as a single gas) at high pressure is most commonly expanded through a Joule-Thomson valve in the end of a probe tip to cause cooling. The drop in pressure across the valve causes the cooling. Because the nitrous oxide is at room temperature until it reaches the probe tip, the insulation requirements of the liquid nitrogen system are not necessary, While this allows for easy miniaturization, greater precision and greater flexibility, cooling to only -79.degree. C. can be achieved, which is not suitable for cancerous or large lesions. Similar to liquid nitrogen, nitrous oxide is also lost during use, and the devices must be used in well ventilated areas due to nitrous oxide narcosis.
It is an object of the invention to provide a novel cryosurgical instrument that would combine the versatility of the nitrous oxide devices with the cooling capacity of liquid nitrogen devices.
It is also an object of the invention to provide a novel cryosurgical instrument wherein the system producing the cooling is preferably in a closed circuit so that the coolant materials can be recirculated, eliminating the need for replenishment.
It is another object of the invention to provide a novel cryosurgical instrument that would utilize a mixed-gas Joule-Thomson refrigeration technology (adiabatic expansion of multiple mixed gases across a valve).
It is an additional object of the invention to provide a novel high cooling capacity (near liquid N2 and much higher than nitrous oxide) Joule-Thomson device with the flexibility and versatility to be employed in endoscopic, percutaneous, and standard cryosurgical procedures.
It is a further object of the invention to provide a novel cryosurgical instrument that could be used in areas that have difficult access to liquid nitrogen.